First Clementine Post

[Shannon Parks]

I asked Tom McNally if he had any ideas for a new project and he requested a Darling PCB. I thought that was curious, as he can whip them up in a couple hours but I saw where he was coming from. Let's take an easy build and make it *easier*. At the time, I was working on a SE 807/1625 amp and I decided to marry these ideas together. So you can build a 3/4W Darling, or use it to build a 4W trioded 6L6 family amp (ie 6L6, 807, 1625, 6BG6). Obviously you can use other pentodes - like an EL34 - but I'm focusing on the 6L6-types right now. I figure if I tweak one, I tweak them all.

Here's the first run with the Darling build. I used Tom's Darling variant. Obviously, many props to the Darling originator, Bob Danielak. All the voltages tested perfect and I got *exactly* 3/4W.

The Clementine is 3" by 8" and .091" thick with 4oz copper - quite stout. I used the newer Hammond 269EX with 125V primary and my variac set to 120V for power. It is a cute transformer! Output transformers are the Edcor GXSE15-8-5K that I got in a trade from Ed Brown (these are the ones he tested in another thread). I think with the GXSE10-8-5K (the smaller 10W version) that it would be feasible to squeeze this all into the Hammond 6x10x2 chassis, in particular, the 1441-16BK3CWW. If not, the 8x12x2 would be a cinch. Parts to stuff the board minus sockets were $22.

Schematic for a 1626 Darling Build of the Clementine

[TerrySmith]

SWEEET! And I just happen to have a bunch of 6L6 tubes to burn up!

[Ty_Bower]

I'm going to batty trying to figure out where you've hidden the rectifier diodes. They must be on the socket side? Looks like a fun project. Didn't have time to take the Edcors out of the boxes? Have you already had a run of boards printed up?

[Shannon Parks]

I'm going to batty trying to figure out where you've hidden the rectifier diodes. They must be on the socket side? Looks like a fun project. Didn't have time to take the Edcors out of the boxes? Have you already had a run of boards printed up?

Indeed, I put the diodes on the opposite side as well as four power resistors. I was worried the Edcors would be scuffed up on my bench so I left them in the box - kind of funny, isn't it? Yes, I skipped the prototype step and went straight into a small run of boards. Probably price them like the Budgie, i.e. $39 plus $2.75 shipping, and free shipping with multiple boards.

BTW, -1dB bandwidth is 26.5Hz to 24.5kHz and -3dB bandwidth is 14.5Hz to 42kHz. Not bad! Measured this with a 1V output into 8 ohms, or 1/8W.

Shannon

[TomMcNally]

This should be a fun little board, perfect for a quick build for newbies, or
for gifts, etc. I've built over 25 Darlings, everyone seems to love 'em.
The Euro connectors will make it real nice too. Using the board as a
template before stuffing the parts, as with other diytube boards, makes
it real easy.

... tom

Here's what a handwired amp would look like ...

[EWBrown]

Very nice! Nice to see a really well designed compact-sized PC board. The Edcor GXSE15-8-5KOPTs look really familiar.

Even without having actually held one of these in my hand, I have already figured out an easy way, from a look at the schematic, to make the Clementine into a single channel "floating paraphase" PP amp And, best of all, no etch "surgery" would be needed.

Two boards would be needed for stereo.

I'll post the details of how to do it once, I have actually tried it out.

Hint, it's the same basic approach which I figured out for the G*S*G.

/ed B

[Ty_Bower]

I used the newer Hammond 269EX... Output transformers are the Edcor GXSE15-8-5K

Hmm... I don't have any surplus transformers laying around (and if you believe that, I've got a bridge to sell). I'm also a big fan of sole sourcing the iron, if for no other reason than to save on shipping costs. What kind of power transformer can I get from Edcor that will be "close enough"? They don't seem to have any 380VCT in their lineup, preferring to go with 360 or 400 volt units. Is it better to err a little on the side of too high a voltage, and burn the extra or idle a little lower? Or should I aim for a slightly low voltage and idle the tubes a little higher to keep dissipation up?

I suppose the correct answer depends on the load I've selected. If I'm not mistaken, the original design was constructed around the Hammond 125E outputs set up for 4K:8 operation. It seems that now we are tending towards slightly higher loads (5K:8), and I'm alright with that. Isn't the general rule of thumb that when you use a higher load, you typically increase the voltage and decrease the current? Yes, I suppose I should draw out the load line and see... and of course, if we're talking about the 6L6 instead of the 1626, that changes things too.

I'm looking at these two power transformers from Edcor:
XPWR165-120/240 $32.46
Power transformer for a 120V or 240V, 50/60Hz. line to 400V (200-0-200) at 50mA center tapped and 12.6V at 2.5A.

XPWR177-0/120/220 $39.53
Power transformer for a 120V and 220V, 50/60Hz. line to 400V at 70mA center tapped and 6.3V at 2.5A center tapped.

And of course, who wouldn't be tempted to try this little output transformer?
GXSE5-8-5.5K $17.22
5W, single ended tube output transformer for 5.5K Ohms to 8 Ohms.

[TomMcNally]

I believe Edcor will make anything you want, custom, for a small
charge ($40), then it stays on their inventory. If you want to think
about that, I'd be happy to pay the one time fee and order a
pair of the new design for future use myself.

I just got a 60 pound Edcor shipment today, plenty of XSE15-8-5K,
my fav!

... tom

[TomMcNally]

Let me clarify, it wasn't ALL XSE15-8-5Ks ...

A custom Clementine (Darling version, not Chubby Clementine)
with 120/240 volt primary would be cool too.

[Shannon Parks]

Ty, those are the two power transformers I was looking at from Edcor. The first one seems like a customer spec'd that exactly for a Darling amp, IMHO. I would maybe have some 1.2K 1W or better resistors as a spare in case the standard 1K cathode resistors were too high of a bias current. In my current setup, the 1626s are idling at 5W. In a related topic, having 1K bias resistors sure makes measuring current easy - handy for matching. Even on the 12SL7!

The 6L6 build will use a B+ of around 400V. I immediately wanted to use the PA774 as it is easy and cheap to acquire, and Edcor has a clone available. The dual 6.3V taps can be swapped around to be in series for 12.6V tubes, namely the 1625 which is a plentiful WWII JAN tube. I haven't spec'd a power tranny for a tube rectified 6L6 Clementine yet. I would probably recommend using using a coke bottle 5V4 and a 700VCT tranny.

Shannon

[EWBrown]

And of course, who wouldn't be tempted to try this little output transformer?

GXSE5-8-5.5K $17.22

5W, single ended tube output transformer for 5.5K Ohms to 8 Ohms.

IIRC, Brian Weston stated that these smaller 5W OPTs were good for at least 34 mA primary current, which would be good to go with 1626s (or even 12B4As).

/ed B

[Geek]

Yeah and that's more I think for magnetic saturation restrictions.... the wire is certainly good for twice that.

Cheers!

[dhuebert]

Sorry, guys. I looked at the schematic and it will never work. It is too simple. Double or triple the parts count and you might have something.

Also I read that cryogenic processes are now necessary for sound perfection.

Don

[Geek]

^^^--- I want a "Like" button for posts like that ---^^^

[Ty_Bower]

Dumb question... is it safe to run a jumper from the "GND" eyelet on the board to the unused center terminal on block J5? I wasn't sure if the space was required to maintain minimum distances on the high voltage traces. It seems like it might be convenient to have the PT center tap easily detached.